Method for the electrophoretic coating of dental substrates

ABSTRACT

The coating of dental substrates, such as the stumps of a working model or implants including ceramics, e.g. alumina, by means of electrophoresis results, especially because of the production of gas, in products unfit for use. It is therefore the aim of the invention to provide a coating method that allows for a high-quality coating of dental substrates in the shortest time possible, irrespective of the material constitution of the substrate. According to the inventive method, the substrate (stump  2 ) is fixated in an insulating mass ( 3 ) in a vertical holder ( 1 ). The substrate is coated with a separating agent and a hygroscopic layer and a further layer is applied thereon by shortly dipping the stump into the slip ( 6 ). The current used for electrophoresis is supplied via the layer ( 7 ) so formed. The inventive method, when used for non-conducting substrates, requires no silver enamel or the like. The method can also be used for conducting substrates, e.g. titanium implants, as the current flows only via the layer ( 7 ).

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a submission to enter the national stage under 35 U.S.C. 371 for international application number PCT/DE2004/001792/ having international filing date 10 Aug. 2004, for which priority was based upon patent application 103 39 603.9 having a filing date of 28 Aug. 2003 in Germany.

(c) STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT

(Not Applicable)

(d) REFERENCE TO AN APPENDIX

(Not Applicable)

(e) BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the coating of a ceramic on a dental substrate by electrophoresis in an aqueous slip.

2. Description of the Related Art

A method is already known from DE 27 05 770 A1 in which an opaque substance from a metal alloy is applied to a substrate (cap) by electrophoresis. The opaque mass is suspended in water so that an aqueous slip is therefore used here. This method has presumably not gained acceptance in practice because of a lack of strength.

A substrate according to the invention is understood to mean any article in dental technology on which a ceramic material is applied.

In the 20-year younger WO 99/50 480 A1, the idea of electrophoresis was taken up again. Here, the inventor became convinced that aqueous suspensions are not suitable for electrophoresis because of formation of hydrogen bubbles, and consequently, the patent teaches work with organic suspensions that, apart from other disadvantages, require significantly higher voltage (50-400 V). According to the single example in this document, a slurry of alumina and ethyl alcohol was produced to make a cap. A duplicate of a tooth stump coated with a silver coating is coated electrophoretically at 100 V and the produced cap then sintered. After sintering, electrophoretic application of glass powder occurs, which, after 5 hours of drying, has infiltrated into the alumina mass.

According to DE 100 214 37 A1, conventional aqueous slips of dental technology are used to produce fully ceramic substructures, especially alumina caps. In this case, the stump of a working model is coated with a separating agent, on which a silver coating according to the practical example is applied. The solids of the slip are electrophoretically precipitated on the silver coating by application of a voltage.

This method has the advantage over the method of WO 99/50480 A1 in that it operates without duplication. It is therefore less time-consuming, has lower material costs, avoids possible errors by eliminating duplication, and requires less time. In addition, water as a suspension agent is not a hazard to health nor is it an explosive, and it permits more rapid transport of ceramic particles. Application of the infiltration glass in WO 99/55480 by electrophoresis is also very troublesome.

A common feature of both instructions, however, is the disadvantageous use of silver lacquer, since experience has shown that an imprecise fit results, in addition to the increased time and material demands. During firing, vapors that are hazardous to health and non-biocompatible residues are also formed, which must be removed from the sintered ceramic in time-consuming fashion. The silver lacquer also has a tendency toward uncontrolled bubble formation. The use of a silver lacquer is fully unsuitable if the ceramic material applied by electrophoresis is to remain on the substrate, as is the case during application of a dentin or cutting mass, since in addition to mechanical weakening, unacceptable visual properties result.

The task of the invention stated in claim 1 is therefore to provide a method that permits electrophoretic coating of dental substrates with the highest precision in the shortest time.

Advantageous variants are described in the dependent claims.

(f) BRIEF SUMMARY OF THE INVENTION

The invention is a method for coating dental substrates with a ceramic by electrophoresis in an aqueous slip and is especially for coating a stump of a working model or an implant abutment with alumina or zirconia. The substrate is fixed in a vertically moving holder in an insulating mass and is coated with a separation agent. A hygroscopic salt layer is applied onto the separation agent. The coated region is dipped into the slip and then the substrate is pulled out from the slip far enough so that, during subsequent application of a voltage, only the part of the substrate to be coated with the ceramic is situated in the slip.

(g) BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The method according to the invention is explained below by means of two drawings. In the drawings:

FIG. 1 shows the production of a cap,

FIG. 2 shows coating of an implant abutment.

(h) DETAILED DESCRIPTION OF THE INVENTION

A vertically movable holder 1 is shown in FIG. 1, on which the stump 2 of a working model is fastened by means of an insulating mass. The holder is connected to the plus pole (not shown) of a power supply and consists of an electrically conducting material. The insulating mass 3 is bridged by a tongue 4 so that the stump 2 can have electrical contact with the plus pole. A separation layer is initially applied to stump 2, as is known for example from DE 198 12 664 A1, which can advantageously be coated with the solids of slip 6, for example, with alumina if the cap being produced is supposed to consist of alumina. A concentrated NaCl solution is then applied to the coated region, which can contain commercial detergents.

The coated region is shaded in FIG. 1 and extends to plane O-O. The stump 2 is then briefly dipped into the container 5 filled with slip 6 up to plane O-O and withdrawn in the depicted position. Only the part of the stump 2 to be coated is still situated in slip 6. The stump 2 therefore has a total layer that, viewed from the inside out, consists of a separation layer, optionally a ceramic powder layer, a hygroscopic salt layer and a slip layer.

After application of a voltage to about 40 V, the stump 2 is connected to the plus pole via tongue 4, whereas the minus pole is formed by the container 5. The conducting salt layer on the non-conducting stump 2 made of gypsum causes a precipitate 8 on the stump. This precipitate 8 is then dried in known fashion, machined by a CNC milling machine, sintered and glass-infiltrated and finished to a cap.

Coating of an implant abutment 12 made of titanium is shown in FIG. 2 and occurs in similar fashion to the coating of a working stump just described. The implant abutment 12 is fastened in a holder 11 by means of an insulating mass 13, for example, conventional molding compound made of a thermoplastic. The implant abutment is shown in the electrophoresis position after it has been dipped into the slip 16 in container 15 up to plane O′-O′. As is apparent from FIG. 2, the layer 17 also covers the lower region of holder 11 up to plane O′-O′. This layer, as in the first example according to FIG. 1, consists of a separation layer, optionally the ceramic powder, an overlying hygroscopic salt layer, which is covered by the slip. During application of the electrophoresis current, precipitate 18 is formed, which is further processed in known fashion.

It is apparent from the above comments that it is irrelevant whether the substrate is conducting or non-conducting, since the electrical resistance is only established by the applied layer. Thus far it has been necessary for the non-conducting substrate to be provided with a silver coating or the like, which leads to the aforementioned drawbacks. Conducting substrates generally lead to uncontrollable gas development with the result that an unusable product is formed.

Because of the versatile application of the method according to the invention, the teachings are not restricted to the production of caps (for example, from alumina) or to coating of implant abutments with dentin mass, since any conceivable dental substrate can be coated with the method according to the invention. Metal substructures can thus also be coated with dentin mass. The application of a cutting mass on dentin is also possible. 

1. A method for coating of dental substrates with a ceramic by electrophoresis in an aqueous slip, characterized by a. fixing the substrate (2; 12) in a vertically moving holder (1; 11) in an insulating mass (3; 13), b. coating the substrate (2; 12) with a separation agent c. applying a hygroscopic salt layer onto the separation agent d. dipping the region so coated into the slip and e. pulling out the substrate from the slip far enough so that during subsequent application of a voltage only the part of the substrate to be coated with the ceramic is situated in the slip.
 2. A method according to claim 1, characterized by supplying current to the substrate via a tongue (4).
 3. A method according to claim 1, characterized by supplying current to the substrate via the applied layer, the layer being in contact with holder (11).
 4. A method according to claim 1, wherein the substrate is a stump (2) made of gypsum.
 5. A method according to claim 1, wherein the substrate is an implant abutment made of titanium or ceramic.
 6. A method according to claim 1, wherein the salt layer contains sodium chloride.
 7. A method according to claim 1, wherein surfactants are added to the salt layer.
 8. A method according to claim 1, wherein dentin or a cutting mass is applied to a metallic or ceramic substrate.
 9. A method according to claim 1, wherein the separation agent is coated with solids of the slip.
 10. A method according to claim 1 and further comprising coating a stump (2) of a working model or an implant abutment (12) with alumina or zirconia during the subsequent application of the voltage. 